Input isolated voltage monitor with voltage tracking

Abstract

A fly-back circuit includes a voltage source, a transformer comprising a primary winding electrically coupled to the voltage source and a secondary winding electrically coupled to a load, a diode connected between the secondary winding and the load, a switch electrically coupled to the primary winding, a controller operable to open and close the switch to control energy transfer from the primary winding to the secondary winding; and a voltage monitor connected to a node between the secondary winding and the diode. The voltage monitor includes a processor that generates a variable threshold tracking voltage (Vthtracking), generates an output signal that is a toggling output when voltage at the node is above Vthtracking and a constant output when the voltage source is operating below Vthtracking and increases Vthtracking when the output signal is toggling until the output signal is not toggling.

What is claimed is: 
     
         1 . A fly-back circuit comprising:
 a voltage source;   a transformer comprising a primary winding electrically coupled to the voltage source and a secondary winding electrically coupled to a load;   a diode connected between the secondary winding and the load;   a switch electrically coupled to the primary winding;   a controller operable to open and close the switch to control energy transfer from the primary winding to the secondary winding; and   a voltage monitor connected to a node between the secondary winding and the diode,   wherein the voltage monitor includes a processor that generates a variable threshold tracking voltage (Vthtracking), and   wherein the voltage monitor generates an output signal that is a toggling output when voltage at the node is above Vthtracking and a constant output when the voltage source is operating below Vthtracking, and   wherein Vthtracking is increased when the output signal is toggling until the output signal is not toggling.   
     
     
         2 . The fly-back circuit of  claim 1 , wherein the processor is a digital signal processor that determines whether the output signal is toggling or not toggling and increases Vthtracking when the output signal is toggling and decreases the output signal is not toggling. 
     
     
         3 . The fly-back circuit of  claim 1 , wherein the voltage monitor includes a comparator that produces the output signal. 
     
     
         4 . The fly-back circuit of  claim 3 , wherein the comparator includes a first input connected to the node and second input connected to Vthtracking. 
     
     
         5 . The fly-back circuit of  claim 4 , wherein the first input is an inverting input and the second input is a non-inverting input. 
     
     
         6 . The fly-back circuit of  claim 5 , further comprising:
 a filter connected between an output of the digital signal processor and non-inverting input that smooths a pulse width modulated signal produced by the digital signal processor to convert the pulse width modulated signal into Vthtracking.   
     
     
         7 . The fly-back circuit of  claim 6 , wherein the filter is an RC circuit. 
     
     
         8 . The fly-back circuit of  claim 4 , further comprising a voltage divider between the node and the first input. 
     
     
         9 . The fly-back converter of  claim 8 , wherein the first input is an inverting input and the second input is a non-inverting input. 
     
     
         10 . The fly-back circuit of  claim 4 , further comprising:
 an RC filter connected between an output of the digital signal processor and non-inverting input that smooths a pulse width modulated signal produced by the digital signal processor to convert the pulse width modulated signal into Vthtracking.   
     
     
         11 . The fly-back circuit of  claim 10 , wherein the filter is an RC circuit. 
     
     
         12 . The fly-back converter of  claim 1 , wherein the controller is a pulse width modulation controller operable to output a sequence of pulses to open and close the switch based on determining that the voltage source exceeds a minimum control voltage. 
     
     
         13 . A method comprising:
 providing with a voltage source an input voltage to a primary side of a fly-back circuit that includes primary winding and a secondary winding;   controlling a switch electrically coupled to the primary winding to transition between an open state and a closed state to control energy transfer from the primary winding to the secondary winding;   monitoring voltage with a voltage monitor connected to the secondary winding at a node, wherein the voltage monitor includes a processor that generates a variable threshold tracking voltage (Vthtracking);   generating and output signal with the voltage monitor that is a toggling output when voltage at the node is above Vthtracking and a constant output when the voltage source is operating below Vthtracking; and   increasing Vthtracking when output signal is toggling and decreasing Vthtracking when the output signal is not toggling.   
     
     
         14 . The method of  claim 13 , wherein the voltage monitor includes a comparator that produces the output signal. 
     
     
         15 . The method of  claim 14 , wherein the comparator includes a first input connected to the node and second input connected to a monitor threshold voltage. 
     
     
         16 . The method of  claim 15 , wherein the first input is an inverting input and the second input is a non-inverting input.